After all, Google engineers were directly involved in developing at least one of the phones (the Nexus S) found to have infringed Apple’s patents, and every one of the accused devices was running Google’s Android operating system — the “stolen product” Steve Jobs had promised two years earlier to destroy.

So why hasn’t Apple sued Google directly?

That’s a good question. Clearly Apple made a strategic decision early on to go after the manufacturers of Android hardware — first HTC, then Motorola, and finally Samsung — rather than the company that designed their software platform.

In retrospect, it was smart move. As Apple laid out its narrative for the jury in its closing arguments Tuesday, the Samsung story was an easy one to tell. Not only had the Korean manufacturer imitated Apple’s designs down to the boxes the devices came in, but it left a paper trail that showed the company scrutinizing every aspect of the iPhone touchscreen for ways Apple’s design decisions could improve Samsung’s products.

“The mountain of evidence presented during the trial,” Apple CEO Tim Cook told employees after the verdict, “showed that Samsung’s copying went far deeper than we knew.”

Whether Google left a similar paper trail remains to be seen. Moreover, Google can claim, as it did when it was sued by Oracle, that Android doesn’t produce any direct revenue for the company, so there can be zero damages. Android may generate billions of ad dollars, but that’s a harder story to sell a jury.

“It’s all about tactics,” says FOSS Patents‘ Florian Mueller. “There’s no reason Apple would have to be afraid of suing Google directly. It’s just tactically more convenient to go against other device makers.”

Meanwhile, Apple’s legal team has plenty on its plate. One of its first tasks after Friday’s big win is to ask for preliminary injunctions that would ban the sale of all of Samsung’s infringing devices. A hearing for that request has been scheduled for Sept. 20. Apple may also want to reassert the patents it withdrew to streamline the case and ask the judge to speed up a second suit it filed against Samsung last January that asserts four more patents — some of which, according to Mueller, are even more powerful than the ones it just won with.

There are dozens of Apple v. Samsung cases around the world yet to be decided, not to mention pending suits against HTC and Motorola Mobility, now a wholly owned subsidiary of Google.

“Apple’s strategy of enforcing patents against other device makers is starting to work out, so it may stay the course,” says Mueller. “It could step up its enforcement against Motorola Mobility and later go against Motorola’s parent company directly.”

But, he adds, “If I were in Apple’s shoes the next company I would sue is not Google, but Amazon, which has an even weaker patent portfolio than Google and sells large volumes of Android-based devices with a subsidies-centric revenue model, which is even more of a threat to Apple’s margins than Google’s advertising-based model.”

UPDATE: Late Sunday, Google released the following statement (via The Verge):

The court of appeals will review both infringement and the validity of the patent claims. Most of these don’t relate to the core Android operating system, and several are being re-examined by the US Patent Office. The mobile industry is moving fast and all players — including newcomers — are building upon ideas that have been around for decades. We work with our partners to give consumers innovative and affordable products, and we don’t want anything to limit that.